Several publications and patent documents are referenced in this application in order to more fully describe the state of the art to which this invention pertains. The disclosure of each of these publications is incorporated by reference herein.
The observation that vasoactive intestinal peptide (VIP) is cleaved by antibodies (Abs) from asthma patients provided early evidence that Abs may possess peptidase activity. This observation has been reproduced independently by Suzuki et al. Autoantibody catalysis is not restricted to catalysis of VIP. Autoantibodies in Hashimoto's thyroiditis catalyze the cleavage of thyroglobulin. Further evidence for autoantibody catalysis has been provided by reports of DNase activity in Abs from lupus patients. The bias towards catalytic antibody (Ab) synthesis in autoimmune disease is supported by observations that mouse strains with a genetic predisposition to autoimmune disease produce esterase Abs at higher levels when compared to control mouse strains in response to immunization with a transition state analog.
Like noncatalytic Abs, peptidase Abs are capable of binding antigens (Ags) with high specificity mediated by contacts at residues from the VL and VH domains. The purified H and L subunits are known to be independently capable of binding Ags, albeit with lower affinity than the parent Ab. X-ray crystallography of Ab-Ag complexes have shown that the VL and VH domains are both involved in binding the antigen (Ag). The precise contribution of the two V domains varies in individual Ab-Ag complexes, but the VH domain may contribute at a somewhat greater level, because CDRH3 tends to be longer and more variable in sequence compared to CDRL3.
The initial complexation of a polypeptide Ag by a peptidase Ab is followed by cleavage of one or more peptide bonds. Just prior to cleavage, contacts with the catalytic residues of the antibody are established with the peptide bond in the transition state. See FIG. 1. The ability to hydrolyze peptide bonds appears to reside in the VL domain. This conclusion is based on the cleavage of VIP by polyclonal autoantibody L chains, monoclonal L chains isolated from multiple myeloma patients and their recombinant VL domains, and recombinant L chains raised by immunization with VIP. The H chains of polyclonal and monoclonal Abs to VIP are capable of VIP binding but are devoid of the catalytic activity. The VH domain can nevertheless influence the peptidase activity by “remote control”, because in binding to VIP remote from the cleavage site, it can influence the conformation of the binding site as shown by the peptidase activity of Fv constructs composed of the catalytic anti-VIP VL domain linked to its VH domain. The anti-VIP VH domain exerted beneficial effects and an irrelevant VH domain exerted detrimental effects on the catalytic activity, as evaluated by the values of VIP binding affinity and catalytic efficiency. The proposed existence of distinct catalytic and antigen binding subsites in catalytic Abs is consistent with data that Abs generally contain large combining sites, capable of accommodating 15-22 amino acids of polypeptide substrates, and that substrate regions distant from the cleavage site are recognized by the Abs. Thus, the VH domain offers a means to control the specificity of the catalytic site.
The present invention provides novel compositions and methods for stimulating production of catalytic antibodies and fragments thereof. Catalytic antibodies with specificity for target antigens provide a valuable therapeutic tool for clinical use. Provided herein are improved methods for identifying, isolating and refining catalytic antibodies for the treatment of a variety of medical diseases and disorders, including but not limited to infectious, autoimmune and neoplastic disease. Such catalytic antibodies will also have applications in the fields of veterinary medicine, industrial and clinical research and dermatology.